1. Field of the Invention
Embodiments of the invention generally relate to an implantable electrode arrangement for cardiological devices, such as cardiac pacemakers, which includes an implant support body, an elongate electrode body with a proximal end and a distal end, at least one electrode with an electrode surface arranged in a region of the distal end of the electrode body and brought into contact with the implant support body, and at least one electric contact line that contacts the electrode.
2. Description of the Related Art
Generally, in the case of implantable electrode arrangements, contact line(s) acts or act similarly to an antenna in the event of irradiation of electromagnetic waves and convert the received energy into heat. A typical example of this problem is the examination of patients fitted with a cardiac pacemaker in magnetic resonance tomographs, which, besides a static magnetic field, also use a high-frequency alternating magnetic field superimposed thereby. If the implantable electrode arrangement is exposed to such an alternating magnetic field, signs of heating appear preferably at the ends of the contact lines running in the implant and are dependent on the amplitude of the irradiated electromagnetic wave and are maximal with formation of standing waves.
Various approaches are presented in prior art to solve the problem of heat appearing in the implant. For example, U.S. Pat. No. 7,363,090 entitled “Band Stop Filter Employing a Capacitor and an Inductor Tank Circuit to Enhance MRI Compatibility of Active Implantable Medical Devices”, to Halperin et al., discloses filter arrangements in the feed line leading to a tip or ring electrode, the feed line being provided in the form of electromagnetic oscillating circuits that are constructed with the aid of conventional R-, C- and L-members. Due to the integration into the contact line, the filter elements of Halperin et al. inevitably influence the functionality of the electrode.
A further basic approach uses shunts, as is disclosed in United States Patent Publication 20080009905 entitled “Electrode System with Shunt Electrode” or U.S. Pat. No. 6,944,489 entitled “Method and Apparatus for Shunting Induced Currents in an Electrical Lead”, both to Zeijlemaker, or U.S. Pat. No. 6,871,091 entitled “Apparatus and Method for Shunting Induced Currents in an Electrical Lead”, to Wilkinson et al. For example, the shunt forms a branching off from the contact line, the branching being insulating for D.C. voltage signals but being able to conduct high-frequency signals due to its design, as is typically implemented by capacitor elements. As discussed in Zeijlemaker and Wilkinson et al, the contact line is thus coupled capacitively to the tissue surrounding the electrode arrangement, such that, in the event of irradiation of a high-frequency signal, the energy received by the contact line is delivered to the surrounding tissue, distributed via the shunt over a larger area. Since the nature of the energy of the irradiated signals is not converted, but in view of the capacitive coupling an electric alternating field is in turn generated, as disclosed in in Zeijlemaker and Wilkinson et al, the achievable dissipation rate for the irradiated energy is limited.